The present disclosure relates to a semiconductor structure and a method of forming the same. More particularly, the present disclosure relates to a back-end-of-the-line (BEOL) interconnect structure including graphene present on exposed sidewall surfaces and a topmost surface of a copper, Cu, structure.
Integrated circuits (ICs) typically include a plurality of semiconductor devices and interconnect wiring. Networks of metal interconnect wiring typically connect the semiconductor devices from a semiconductor portion of a semiconductor substrate. Multiple levels of metal interconnect wiring above the semiconductor portion of the substrate are connected together to form a back-end-of-the-line (BEOL) interconnect structure. Within such a structure, metal lines run parallel to the substrate and metal vias run perpendicular to the substrate.
Two developments in the last decade have contributed to increased performance of contemporary ICs. One such development is the use of copper as the interconnect metal of the BEOL interconnect structure. Copper is advantageous because it has a higher conductivity compared with other traditionally used interconnect metals such, as for, example, aluminum.
A second development is the employment of low dielectric constant (low k) dielectric materials and/or air gaps within the BEOL interconnect structure. Low k dielectric materials and air gaps have dielectric constants that are lower than those of traditionally used interconnect dielectric materials such as, for example, silicon dioxide.
One problem of using copper as the metal in the BEOL interconnect structure is that copper is very reactive in air and readily forms a copper oxide. As such, exposed copper surfaces need to be passivated. Typically, a dielectric and/or metallic capping layer are employed in prior art copper-containing BEOL interconnect structures.
Another problem that arises when copper is used as the metal in the interconnect structure is that copper ions tend to diffuse into the interconnect dielectric material during use. The diffusion of copper ions from the metal feature into the dielectric material causes voids to form within the metal feature of the BEOL interconnect structure. These voids can lead to failure of the IC. As such, a diffusion barrier such as, for example, TiN, is typically used to reduce the diffusion of copper ions into the interconnect dielectric material and thus reduce the electromigration of copper from the metal feature.
Although various capping layers and diffusion barriers are known in the art, a need exists to provide an alternative material that can provide the same functions as the capping layers and the diffusion barriers mentioned above, yet reduce the resistivity of the copper metal within such BEOL interconnect structures.